1. Field of Invention
The present invention relates to shape detection methods and apparatuses for a hot strip mill, and more particularly, to a shape detection device and method used in conjunction with a pinch roll assembly and a hot strip reversing mill or mills.
2. Background Art
During the hot rolling of metal strip, such as steel, the rolling process can cause undesirable shape defects in the profile and flatness along the width of the metal strip. This generally results from internal stress differentials within the strip which appear during reduction in a hot strip reversing mill having coiler furnaces on opposite sides. As the need for improved shape is ever present from a mill, techniques are required to ensure the desired shape is achieved during the reduction of the metal strip.
These shape defects can be greatly minimized and often avoided by applying shape control techniques in controlling the rolls of the mill. Shape control techniques include adjustments at the reversing stand of roll bending, screw down positions and roll shifting. Also, it is important to control the steering of the metal strip between the rolls at the reversing stand to keep the metal strip tracking on mill center.
In order to apply the shape control techniques, the operator must be able to detect when the process is causing the shape defects or when the metal strip tracks off mill center. Currently, the operator visually checks for defects caused by the process and to ensure that the metal strip is tracking on mill center. The operator then must adjust the mill manually using the shape control techniques to correct for defects and adjust steering of the metal strip if the metal strip is off mill center.
Pressure transducers and load cells have been used on each side of the reversing stands to detect force differentials between the stand sides to indicate the metal strip is tracking off mill center. The use of pressure transducers or load cells can be unreliable because strip geometry, temperature changes in the metal or hardness of the metal can also cause force differentials that can be detected by the pressure transducers or the load cells.
Today, automated shape control systems using computer technology can control shape and steering of the metal strip with the use of shape control sensors. Shape control sensors detect metal strip position and shape defects throughout the metal strip. The shape control system uses the data from the sensor for monitoring and continuously correcting the flatness of the metal strip. The automated shape control system relieves the operator from visually checking for defects and manually making changes to the process. Such systems and shape control sensors are described in U.S. Pat. Nos. 3,459,019; 3,688,571; 4,289,005; 4,356,714; 4,428,244; 4,512,170; 4,700,557; 4,809,527; 4,809,528; 4,860,212; 4,964,289; 5,089,776; 5,231,858; 5,267,170; 5,285,684; and 5,400,258.
The problem that arises is that shape control sensors must be incorporated into the design of a mill. Shape control sensors can be a contact or non-contact shapemetering device as discussed in the above-mentioned patents. Each type of shapemetering device has the sole purpose of detecting shape defects in the metal strip and has been used in cold strip mills. Currently for Steckel and other hot strip reversing mills, an operator still checks for shape defects visually and makes manual adjustments to the mill. Visual detection by an operator is still employed because the mills already in operation are generally restricted to the space available to add a contact or non-contact shapemetering device. Non-contact shapemetering devices are not used because their size does not allow them to be located near the rolls of the reversing stand where the reduction process takes place. Contact shapemetering devices are not used because it could prove to be a complicated and costly process to add a device to current mill designs that can make contact with the metal strip under tension.
Therefore, it is an object of the present invention to integrate a sensor for shape control and steering of the metal strip into existing hot strip reversing mills with minimal modification to the mill design as well as provide new mills with the same advantage.